1. Field of the Invention
The present invention relates to a hybrid type construction machine using both an engine power and an electric power.
2. Description of the Related Art
There is conventionally known a hybrid construction machine such as a hybrid shovel. For example, Japanese Patent Application Laid-Open No. 2000-283107 discloses a construction machine including a hydraulic pump, a generator-motor, an engine which is a power source for driving the hydraulic pump and the generator-motor, a hydraulic actuator which is driven by a hydraulic fluid delivered by the hydraulic pump, an electrical storage device which is charged with an electric power generated by the generator-motor, and a slewing electric motor which is driven by the electric power stored in the electrical storage device.
According to the construction machine, there is a possibility of ignition or fail of the electrical storage device due to an increase in a charging rate of the electrical storage device beyond an upper limit, namely, overcharging. Consequently, there is need for controlling a charge amount of the electrical storage device so as to prevent the charging rate of the electrical storage device from exceeding the upper limit.
However, regulating the charging rate of the electrical storage device in a prescribed range under all the conditions narrows a range of the charging rate and hinder the hybrid type construction machine from sufficiently achieving its performance. Furthermore, it involves a problem of impossibility of using a full capacity of the electrical storage device and obtaining an energy-conservation effect.